With reference to FIGS. 2 and 3, one prior art embodiment of a heat exchanger is shown. Condenser includes a plurality of adjacent, essentially flat tubes 3 having an oval cross-section and open ends which allow refrigerant fluid to flow therethrough. Flat tubes 3 are fixedly connected to header pipes 2a and 2b, respectively and have a plurality of fluid paths 9 formed by a plurality of partitions 8. Partition wall 7 is disposed in header pipe 2a so as to divide its interior into upper and lower cavities. Inlet pipe 5 is connected to the upper portion of the upper cavity and outlet pipe 6 is connected to the lower portion of the lower cavity.
In operation, compressed refrigerant gas from an external compressor coupled to inlet pipe 5 flows into the upper cavity of header pipe 2a through the inlet pipe, and is distributed so that a portion of the gas flows through each of flat tubes 3 which is disposed above the location of partition wall 7, and into the upper cavity of header pipe 2b. Thereafter, the refrigerant in the upper cavity of header pipe 2b flows downwardly into the lower cavity thereof, and is distributed so that a portion of the refrigerant flows through each of flat tubes 3 disposed below the location of partition wall 7, and into the lower cavity of header pipe 2a. As the refrigerant gas sequentially flows through flat tubes 3, heat from the refrigerant gas is exchanged with the atmospheric air flowing through corrugated fin units 4. The condensed liquid refrigerant in the lower cavity of header pipe 2a flows out of the cavity through outlet pipe 6 and into an external receiver coupled to the header pipe.
Referring further to FIG. 4, the temperature of the refrigerant flowing through each flow path 9 of flat tubes 3 and the temperature of the heat-exchanging air is shown in relation to the distance from the windward side of the heat-exchanging air is shown.
Since the refrigerant in fluid paths 91 at the windward side is heat-exchanged with the heat-exchanging air which has not yet been used for heat exchanging, i.e., the air is at a low temperature, there is a large temperature difference between the temperature of the refrigerant and the temperature of the heat-exchanging air. Accordingly, the heat-exchanging efficiency of the condenser at the windward side becomes high. On the other hand, since the refrigerant in fluid paths 92 at the leeward side is heat-exchanged with the heat-exchanging air which has already been used for heat-exchanging, i.e., the air is at a relatively high temperature, there is not a large temperature difference between the temperature of the refrigerant and the temperature of the heat-exchanging air. Accordingly, the heat-exchanging efficiency of the condenser on the leeward side decreases.
As mentioned above, there is a large difference in the amount of heat-exchanging occurring on the windward side and on the leeward side of the heat exchanger and, thus, the total amount of heat-exchanging in such a conventional heat exchanger becomes small.
In addition, since the efficiency of a heat exchanger is determined by the amount of heat-exchanging and the pressure loss in the heat exchanger, when the amount of heat-exchanging is large and the pressure loss within the heat exchanger is small, the efficiency of the heat exchanger is improved. However, the amount of heat-exchanging and the pressure loss are directly proportional to each other. If the amount of heat exchanging becomes large, the pressure loss also becomes large. Accordingly, although the heat exchanger is designed so that the amount of the heat-exchanging and the pressure loss can be balanced, since the pressure of the refrigerant gas discharged from a compressor in an automotive air conditioning system and the rotational speed of the compressor are changed according to the driving condition of the automobile, it is very difficult to balance the amounts of heat-exchanging and pressure loss.